Naturally occurring communication very often takes the form of discourse such as, for example, a friendly conversation. The success of conversations that serve social as well as informational purposes is largely determined by whether the participants obey the rules governing polite discourse. Inappropriate comments or word choices can divert attention from the literal message and, more importantly, can undermine the social bond between the people speaking. Abiding by these conventions requires understanding what affects the feelings other people, keeping track of what other people know and do not know, and knowing what is appropriate in different discourse settings defined by people's feelings and knowledge. The effects of unilateral brain injury on patients' success with these aspects of discourse. The patients of most interest are those who have sustained right hemisphere brain damage (RHD) due to stroke but who do not have aphasia. Non brain-damaged control subjects will provide the primary comparison group in light o the heavy linguistic demands of most of the proposed tasks, but right and (nonaphasic) left prefrontally damaged patients will be tested when possible to provide information on localization of function, as will aphasic LHD patients with middle cerebral artery territory lesions. Results from the planned studies will provide a window onto the mental life of the brain-injured individual and will help. us understand the ways in which brain injury impairs social reasoning which is a major source of difficulty for RHD patients and their families.